Rotary piston pump end pressure regulation system

ABSTRACT

A rotary piston pump for fluids, wherein the ends of the housing are configured so as to provide reduced pressure differentials between opposite sides of the rotor end disks.

FIELD OF THE INVENTION

The present invention relates to pump end pressure regulation systemsfor use in rotary piston pumps.

BACKGROUND OF THE INVENTION

Rotary pistons pumps, in the nature of encased rotors with rotor disksat the rotor ends and vanes between those rotor disks, which vanes moveradially in and out of the rotors depending upon their location withinthe casing, are known.

One such device is described in U.S. Pat. No. 6,554,596 of Albert andDavid Patterson, issued Apr. 29, 2003, in which the vane movement, inand out of the rotor, is achieved by cam surfaces within the casing,which surfaces act on both inner and outer edges of the vanes.

In applicant's co-pending U.S. patent application Ser. No. 10/680,236entitled rotary pistons, the outward movement of the vanes is achievedby upward extensions of shoulders at the sides of each vane, whichupward extensions contain pins which are seated in races continuouslyextending in portions of the interior side wall of the casing andpositioned so that as the pins move about the races, they draw theirrespective vanes outwardly and inwardly.

Other known constructions of such rotary pistons require centrifugalforce, through rotation of the rotor, to force the vanes outwardly. Forinstance, in applicant's U.S. Pat. No. 6,896,502, issued May 24, 2005,three planar vanes are seated in rotor slots formed along chords, whenthe cylindrical rotor is viewed in lateral cross-section, those slotsbeing oriented so that the planes of adjacent vanes lie at 60° angles toeach other.

In applicant's co-pending U.S. patent application Ser. No. 10/680,236,filed Oct. 8, 2003, outward movement and maintenance of the outwardpositioning of the vanes is assisted by biasing means, for examplesprings.

Such rotary piston pumps are constructed to move fluids at relativelyhigh pressure. Those portions of the rotor disks as they pass in thevicinity of the pump intake port, are under significantly lower pressurethan those portions which are upstream from the outlet port, which areoften under significantly higher pressure. When operating under suchhigh pressure conditions, this pressure differential may cause the rotordisks to distort, significantly affecting the efficiency of operation ofthe pump and reducing the usable lifespan of pump components such as therotor disks.

It is an object of the present invention to provide a rotary piston pumpthat reduces the pressure differentials acting on the rotor disks. It isa further object, of one embodiment of the present invention, to providea rotary piston pump that uses fluid pressure within the pump to assistin movement of the vanes.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a rotarypiston pump comprising a shaft to rotate about a longitudinal axis. Arotor is centrally secured to the shaft, the rotor having a body with acylindrical surface extending between spaced ends. A rotor disk issecured at each end of the rotor and each rotor disk is secured at acenter to the shaft. A housing encases the rotor and the rotor disks andportions of the shaft within an internal cavity. The housing hasinterior end walls adjacent to, but spaced from, the corresponding rotordisks to form an end space therebetween, and an interior sidewall, withfluid inlet and fluid outlet ports in the interior sidewall. A firstportion of the interior sidewall of the housing is cylindrical andcurved with a constant radius over an angle of about approximately 180°.The first portion is spaced a constant distance from confrontingportions of the cylindrical surface of the rotor. A second portion ofthe interior sidewall of the housing extends between the extremities ofthe first portion of the interior sidewall. The curvature of the secondportion has a greater radius than a curvature of the first portion. Thecylindrical surface of the rotor is proximal to the interior sidewall ofthe housing at a point between the fluid inlet and fluid outlet portsabout midway along the second portion. The fluid inlet and fluid outletports are located in this second portion of the interior sidewall of thehousing. Two or more equally spaced, radially oriented slots in therotor longitudinally extend across the cylindrical surface of the rotorbody. Two or more similar vanes are provided, each vane having internaland external edges extending between sides. Each vane is slidably seatedin one of said slots, movable radially in the corresponding slot betweenan extended position with the external edge of the vane adjacent theinterior sidewall of the housing, and a retracted position wherein theexternal edge of the vane does not extend beyond the cylindrical surfaceof the rotor. The vanes are spaced from adjacent vanes about the rotorsuch that there is always a vane positioned between the fluid inlet andfluid outlet ports. Means are associated with the vanes to enable thevanes to move to extended position. A plurality of slots in the rotordisks are aligned with the rotor slots and slidably receive the sides ofthe vanes. The rotor disks, the housing and the vanes are constructed sothat, during operation of the rotary piston pump, fluid entering thehousing through the inlet port is carried by the rotor, in each of thecompartments formed between adjacent vanes, the rotor surface betweenthe vanes, the rotor disks and the corresponding portions of the endwalls and interior sidewall of the housing, until the adjacent vanesencompass the outlet port where the fluid is allowed to leave thehousing. At least one aperture is provided in each compartment througheach rotor disk to permit fluid communication from the compartment tothe end space, thereby to permit equalization of fluid pressure in thecompartment and in the end space. The end space between each of thecorresponding housing end walls and rotor disks are provided withpartition sections extending in a line between the fluid inlet and fluidoutlet ports and dividing that end space into two sub-sections. Thepartition sections are constructed so as to withstand pressuredifferentials between the sub-sections on either side of the partitionsections.

In accordance with an alternative embodiment of the present inventionthere is provided a rotary piston pump comprising a shaft to rotateabout a longitudinal axis. A rotor is centrally secured to the shaft,the rotor having a body with a cylindrical surface which extends betweenspaced ends. A rotor disk is secured at each end of the rotor and eachrotor disk is secured at a center to the shaft. A housing encases therotor and rotor disks and portions of the shaft within an internalcavity, the housing having interior end walls adjacent to thecorresponding rotor end disks, and an interior sidewall, with fluidinlet and fluid outlet ports in the interior sidewall. A first portionof the interior sidewall of the housing is cylindrical and curved with aconstant radius over an angle of about approximately 180°. The firstportion is spaced a constant distance from confronting portions of thecylindrical surface of the rotor. A second portion of the interiorsidewall of the housing extends from the extremities of the firstportion of the interior sidewall. The curvature of the second portionhas a greater radius than the curvature of the first portion. Thecylindrical surface of the rotor is proximal to the interior sidewall ofthe housing at a point between the fluid inlet and fluid outlet portsabout midway along the second portion. The fluid inlet and fluid outletports are located in the second portion of the interior sidewall of thehousing. Two or more equally spaced, radially oriented slots in therotor longitudinally extend across the cylindrical surface of the rotorbody. Two or more similar vanes are provided, each vane having internaland external edges extending between sides. Each vane is slidably seatedin one of said slots, movable radially in the corresponding slot betweenan extended position with the external edge of the vane adjacent theinterior sidewall of the housing, and a retracted position is providedwherein the external edge of the vane does not extend beyond thecylindrical surface of the rotor. The vanes are spaced from adjacentvanes about the rotor such that there is always a vane positionedbetween the fluid inlet and fluid outlet ports. A plurality of slots inthe rotor disks are aligned with the rotor slots and slidably receivethe sides of the vanes. The rotor disks, the housing and the vanes areconstructed so that, during operation of the rotary piston pump, fluidentering the housing through the inlet port is carried by the rotor, ineach of the compartments formed between adjacent vanes, the rotorsurface between the vanes, the rotor disks and the correspondingportions of the end walls and interior sidewall of the housing, untilthe adjacent vanes encompass the outlet port where the fluid is allowedto leave the housing. A pair of configured depressions is positioned ineach of the end walls, open towards the corresponding rotor disk. Portsat the bottoms of the slots in the rotor disks pass through the rotordisks to provide fluid communication between the lower portions of therotor disk slots below the vanes and the configured depressions. Atleast one aperture is provided in each compartment through each rotordisk, the apertures and configured depressions positioned to beintermittently aligned, during operation of the pump, so as to permitequalization of fluid pressure in the compartment and in the configureddepressions when the apertures are in alignment with the configureddepressions. The configured depressions are configured so as to deliver,during operation of the pump, the lesser pressure of fluid drawn intothe compartments from the inlet port through the slots below the vanesas the vanes pass over part of the second portion of the interiorsidewall adjacent to the outlet port so as to urge those vanes inwardlytowards retracted position, and to deliver the greater pressure of thefluid carried in the compartments between the inlet and outlet portsthrough the slots below the vanes when the vanes are approaching theinlet port and passing over the constant radius portion of the sidewall,so as to urge those vanes outwardly towards extended position.

The rotary piston pump, in accordance with the present invention, allowsfluid pressures within the compartments between the vanes to bereplicated on the outside of the rotor disks, between the rotor disksand the ends of the housing, thereby avoiding deflecting or distortionof the rotor disks due to pressure differentials. As well, in oneembodiment of the present invention, the pressure differentials existingin the fluids between compartments are used to facilitate the inward andoutward movement of the vanes in the rotor vane slots.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages of the invention will become apparent uponreading the following detailed description and upon referring to thedrawings in which:

FIG. 1 is an exploded perspective view of an example embodiment of therotary piston pump according to the present invention;

FIG. 2 is a perspective view, partially exploded and in partial section,of the rotary piston pump of FIG. 1;

FIG. 3 is a schematic side section view of a further example embodimentof a portion of the rotary piston pump according to the presentinvention;

FIG. 4 is a schematic side section view of yet a further exampleembodiment of the rotary piston pump according to the present invention;

FIG. 5 is a perspective view of an end wall, from the interior, of thehousing of the pump of FIG. 4;

FIG. 6 is a perspective view of a rotor disk of the pump of FIG. 4;

FIG. 7 is a schematic side view of the interior of the pump of FIG. 4,illustrating more clearly certain aspects of the operation of the pump;and

FIG. 8 is a longitudinal section view of a portion of the pump alongline 8-8 of FIG. 4;

While the invention will be described in conjunction with illustratedembodiments, it will be understood that it is not intended to limit theinvention to such embodiments. On the contrary, it is intended to coverall alternatives, modifications and equivalents as may be includedwithin the spirit and scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

In the following description, similar features in the drawings have beengiven similar reference numerals.

Turning to FIG. 1, there is illustrated a rotary piston pump 2 accordingto the present invention. Pump 2 comprises a shaft 4 rotating about alongitudinal axis A-A. A rotor 6 is centrally secured to shaft 4. Rotor6 has a body with a cylindrical surface 8 extending between spaced ends10. A rotor disk 12 is provided at each end of rotor 6, secured at itscenter to shaft 4 and to the corresponding end 10 of rotor 6. Shaft 4,rotor 6 and rotor disks 12 may be of integral construction.

A housing 14 encases shaft 4, rotor 6 and rotor disks 12 within aninternal cavity 16. Shaft 4 extends outside housing 14, as illustrated.Housing 14 has end walls 18 adjacent to but spaced from rotor disks 12,and an interior sidewall 20. Fluid inlet port 22 and fluid outlet port24 are provided in interior sidewall 20.

As can be seen in FIG. 3, first portion 26 of the interior sidewall 20is cylindrical and curved with constant radius over an angle of about180°. This portion is spaced a constant distance from correspondingportions of the cylindrical surface 8 of rotor 6. A second portion 28 ofthe interior sidewall 20 extends between the extremities of this firstportion 26 of the interior sidewall. The second portion 28 has acurvature of greater radius than that of the first portion. (While FIG.3 illustrates a different embodiment, this interior wall configurationis similar in the embodiment of FIGS. 1 and 2.)

Two or more (four are illustrated) equally spaced, radially orientedslots 30 in rotor 6 extend across its cylindrical surface 8. Thiscylindrical surface 8 is proximal to the interior sidewall 20 of thehousing 14 at a point 32 on portion 28, about midway between the inletand outlet ports 22 and 24. Inlet and outlet ports 22 and 24 are locatedin this second portion 28.

Two or more (again, four are illustrated) similar vanes 34 are slidablyseated in the slots 30 of rotor 6 as illustrated. Each vane 34 has aninternal edge 36 and an external edge 38 extending between sides 40 ofthe vanes. Each vane 34 is movable radially in its corresponding slotbetween an extended position with the external edge 38 of the vaneadjacent first portion 26 of the interior sidewall of the housing and aretracted position when the vane reaches point 32, where that externaledge 38 is retracted and does not extend beyond the cylindrical surfaceof the rotor. The vanes 34 are spaced from each other about the rotorsuch that there is always at least one vane positioned between the inletand outlet ports 22 and 24.

In the embodiment illustrated in FIGS. 1 and 2, an ear 42 extends beyondthe external edge 38 of each vane 34 at each of its sides 40. A pin 44is secured to each ear 42 and extends inwardly, as illustrated towardsthe pin on the other ear 42 of that vane. That pin 44 for each ear isseated in one of a pair of oppositely facing races or grooves 46 whichare formed in portions of the interior sidewall 20 of housing 14. Eachrace 46 is continuous and circumscribes the shaft 4 so as to provideproper extending and retracting movement of the vanes as itscorresponding pins move along it during rotation of the rotor.

As can be seen in FIG. 1, a plurality of slots 48 are provided in rotordisks 12. These slots 48 are aligned with corresponding rotor slots 30and slidably receive the sides 40 of the vanes 34 and theircorresponding ears 42. Ears 42 are seated flushly in slots 48 so thattheir confronting surfaces are flush with and do not extend beyond theinner surface of their corresponding rotor disk 12.

The rotor 6, housing 14 and vanes 34 are constructed so that, duringoperation of the pump, liquid or gas entering housing 14 through inletport 22 is carried by the rotor 6, in compartments 50 formed betweenadjacent vanes 34, the rotor disks 12 and rotor surface 8 between thosevanes and confronting portions of the sidewall 20 and end walls 18 ofhousing 14, until the adjacent vanes encompass the outlet port 24 wherethe fluid is allowed to escape.

As can be seen in FIG. 1, it is preferred that a series of apertures 60be provided through each rotor disk at least one such aperture beingpositioned in each quadrant of the rotor disk between each pair ofadjacent slots 48. Each aperture 60 permits equalization of pressurebetween each compartment 50, and the end space 62 between the outer end64 of rotor disk 12 and the facing portion of the end wall 18 of housing14. A pair of annular dam seals 68, constructed as illustrated in FIGS.1 and 2 are seated peripherally beyond these apertures 60 and on thisexterior side of rotor disk 12. The transverse portion 70 of each damseal 68 divides each end space 62 into two sub-sections. (Depending uponthe application, the dam seals could be configured to divide each endspace 62 into more than two sub-sections. However, there would never bemore such sub-sections than the number of compartments 50.) In this way,pressure in each of the sub-sections of end space 62 is equalized withthe pressure of the fluid in the corresponding compartment orcompartments 50 on the other side of the respective aperture orapertures 60 extending through rotor disk 12.

In particular, the pump construction illustrated in FIGS. 1 and 2 allowsthe higher pressures of fluid in compartments 50 as vanes 34 pass theconstant radius, first portion 26 of interior sidewall 20, up to thedischarge port, and the lower pressures in compartments 50 as they passthe outlet port 24 and fluid inlet port 22, to equalize on the otherside of the corresponding end disk 14, in the relevant segment of endspace 62. Since dam seals 68 and portions 70 are arranged to allow partof rotor disks 12 to have high pressure matching the outlet portpressure of the fluid and the other part of the disk to have lower orzero pressure matching that of the inlet port 22, deflection of the enddisks due to pressure differentials is avoided. Transverse portion 70also restricts fluid from going from outlet port 24, through apertures60 and end space 62, into inlet port 22, and avoids the need of reedvalves in apertures 60, as was previously required in the rotary pistondescribed and illustrated in applicant's previously mentionedapplication Ser. No. 10/680,236.

Turning to FIG. 3, there is illustrated an alternative embodiment ofrotary piston pump according to the present invention, in which externalactivation of vanes 34, and ensuring those vanes are always in contactwith corresponding portions of inner sidewalls 20 of housing 14, is bymeans of biasing from springs 76. These springs are held in pockets 78which extend inwardly, as illustrated, from the internal edge 36 of vane34. Two or more such springs 76 and pockets 78 may be provided, in whichcase they are located in spaced fashion from side to side in each vane34. Secured to the bottom of each slot 30 in rotor 6, and positioned tobe mateably received in vane pockets 78, are dowels 80. Springs 76 areheld within pockets 78 by these dowels 80, and bear against the pins andthe bottoms of the respective pockets so as to provide appropriateupward bias to the vanes in their corresponding rotor slots 30. Duringoperation, the outer edge 38 of each vane 34 is constantly positionedagainst a corresponding portion of the interior side wall 20 of housing14. Again the rotor 6, housing 14 and vanes 34 are constructed so that,during operation of the rotary piston, fluid entering housing 14 iscarried by rotor 6 in compartments 50 formed between adjacent vanes 34,rotor cylindrical side wall 8 between those vanes, the rotor disks 12and the corresponding portions of the interior side wall 20 of housing14, until these adjacent vanes encompass the outlet port 24, at whichpoint fluid in that compartment 50 is allowed to escape through outletport 24.

In this illustrated embodiment, the transverse portions 70 of the damseals within end space 60 have a somewhat different configuration thanin the embodiment of FIGS. 1 and 2, although they still extend along aline between the fluid inlet port 22 and outlet port 24.

In the embodiment illustrated in FIGS. 4 to 7, although the rotor androtor disk construction is similar to the embodiment of FIG. 3, thespring and dowel arrangement for the vanes is optional and may not berequired. As well, as can be seen in FIG. 6, holes 82 are formed at thebottom of rotor disk slots 48 as illustrated. As can be seen in phantomin FIG. 4, and more clearly in FIG. 5, a pair of mutually exclusive,configured depressions 84 and 86 are positioned on the inner surfaces ofeach of the end walls 18 as illustrated. Depressions 84 and 86 may bemachined in the inner surfaces of end walls 18, or may be formed in aflat piece which is subsequently welded or otherwise secured to thatinterior surface of end wall 18.

The apertures 60 in end disks 40 are positioned so that as appropriate,they communicate with these depressions 84 and 86. Depression 84 isconfigured to be the low pressure depression so as to deliver, duringoperation of pump 2, the pressure of fluid being drawn into compartments50 from the inlet 22 through the corresponding holes 82 below the vanes34, as vanes 34 pass over the portion 28 of the interior sidewall 20,until the vanes reach point 32. In this manner pressure is reduced inrotor slots 30, below vanes 34 so as to assist the vanes as they aremoved to retracted position over this portion of travel of the vanes. Aswell, this low pressure depression 84 is configured so as to communicatewith apertures 60 of rotor disks 12 of compartments 50 as theircorresponding vanes 34 travel from this point 32 over the rest ofportion 28. In this manner, equalization of fluid pressure on eitherside of rotor disks 12 between compartments 50 and low pressuredepression 84 is permitted.

Depression 86, being the depression for high pressure, is configured soas to permit alignment of holes 82 in the lower ends of rotor disk slots48 so that these holes 82 will be in alignment with depression 86 whenthe corresponding vanes 34 and compartments 50 are traveling from point32, past inlet port 24 and over much of the first portion 26 of theinterior sidewall. Over this portion of travel, the compartments 50 areat high pressure. Accordingly, high pressure is passed throughappropriately positioned apertures 60 through rotor disks 12, into highpressure depression 86, and through holes 82 into the lower portions ofrotor slots 30 below the relevant vanes 34, thereby assisting inextending and maintaining those vanes 34 in their fully extendedpositions as they travel over first portion 26 of the interior sidewall.As well, apertures 60 ensure an equalization of high pressure, asappropriate, on opposite sides of rotor disk 12.

A pressure screw 88 (FIGS. 7 and 8) is provided in a correspondingaperture in end walls 18 of housing 14, permitting partial closure ofthe low pressure depression 84 as illustrated, allowing adjustment ofthe pressure from midrange to low within this depression. This pressurescrew 88 may be in the form of a threaded bolt in from the outside ofend wall 18 of housing 14. This bolt taps into low pressure depression84 adjacent to inlet port 22, as illustrated, and allows adjustment soas to partially close off low pressure depression 84. This adjustablerestriction allows high pressure in rotor slots 30, when they arealigned so as to exhaust into low pressure depressions 84, to losepressure more slowly, resulting in a mid-pressure between the highpressure of outlet port 24 and the low or zero pressure of inlet port22. The adjustable mid-range pressure will be of advantage in someinstances so as to avoid the vanes being urged into their retractedposition less aggressively and related banging of vanes into rotor slots30.

It will be understood that for a particular application, the embodimentof FIGS. 5 to 7 may be provided on one end of housing 14, and the otherend provided with the dam seal 68/70 construction of FIG. 1 or 3.

Furthermore, it will be understood that the present invention hasapplication to many different constructions of rotory piston pumpbesides those specifically illustrated herein, including, for example,the fluid cannon positive displacement pump described and illustrated inapplicant's previously mentioned U.S. Pat. No. 6,896,502, the contentsof which are incorporated herein by reference.

Thus, it is apparent that there has been provided in accordance with theinvention an improved rotary piston pump end pressure regulation systemthat fully satisfies the objects, aims and advantages set forth above.While the invention has been described in conjunction with illustratedembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art in light ofthe foregoing description. Accordingly, it is intended to embrace allsuch alternatives, modifications and variations as fall within thespirit and broad scope of the invention.

1. A rotary piston pump comprising: a shaft to rotate about alongitudinal axis; a rotor centrally secured to the shaft, the rotorhaving a body with a cylindrical surface extending between spaced ends;a rotor disk secured at each end of the rotor, each rotor disk securedat a center to the shaft; a housing encasing the rotor and the rotordisks and portions of the shaft within an internal cavity, the housinghaving interior end walls adjacent to, but spaced from, thecorresponding rotor disks to form an end space therebetween, and aninterior sidewall, with fluid inlet and fluid outlet ports in theinterior sidewall, a first portion of the interior sidewall of thehousing being cylindrical and curved with a constant radius over anangle of about approximately 180°, the first portion being spaced aconstant distance from confronting portions of the cylindrical surfaceof the rotor, and a second portion of the interior sidewall of thehousing extending between the extremities of the first portion of theinterior sidewall, and a curvature of the second portion having agreater radius than a curvature of the first portion, the cylindricalsurface of the rotor being proximal to the interior sidewall of thehousing at a point between the fluid inlet and fluid outlet ports aboutmidway along the second portion, the fluid inlet and fluid outlet portsbeing located in this second portion of the interior sidewall of thehousing; two or more equally spaced, radially oriented slots in therotor longitudinally extending across the cylindrical surface of therotor body; two or more similar vanes, each vane having internal andexternal edges extending between sides, each vane slidably seated in oneof said slots, each vane movable radially in the corresponding slotbetween an extended position with the external edge of the vane adjacentthe interior sidewall of the housing, and a retracted position whereinthe external edge of the vane does not extend beyond the cylindricalsurface of the rotor, the vanes being spaced from adjacent vanes aboutthe rotor such that there is always a vane positioned between the fluidinlet and fluid outlet ports; means associated with the vanes to enablethe vanes to move to extended position; a plurality of slots in therotor disks aligned with the rotor slots and slidably receiving thesides of the vanes; the rotor disks, the housing and the vanesconstructed so that, during operation of the rotary piston pump, fluidentering the housing through the inlet port is carried by the rotor, ineach of compartments formed between adjacent vanes, the rotor surfacebetween the vanes, the rotor disks and the corresponding portions of theend walls and interior sidewall of the housing, until the adjacent vanesencompass the outlet port where the fluid is allowed to leave thehousing, at least one aperture being provided in each compartmentthrough each rotor disk to permit fluid communication from thecompartment to the end space, thereby to permit equalization of fluidpressure in the compartment and in the end space; and the end spacebetween each of the corresponding housing end walls and rotor disksbeing provided with partitioned sections extending in a line between thefluid inlet and fluid outlet ports and dividing that end space into twoor more sub-sections, the partition sections constructed so as towithstand pressure differentials between the sub-sections on either sideof the partition sections.
 2. A pump according to claim 1, wherein themeans to enable the vanes to move to extended position comprise springsurging the vanes to that position.
 3. A pump according to claim 1,wherein the means to enable the vanes to move to extended positioncomprise upward extensions of shoulders at the sides of each vane, whichupper extensions contain pins seated in races continuously extending inportions of the interior sidewall of the housing and positioned so that,as the pins move about the races, they move their respective vanesoutwardly.
 4. The rotary piston device according to claim 1, wherein therotor is provided with four slots, and four vanes, one of said vanesbeing slidably seated within each slot of the rotor.
 5. The rotarypiston device according to claim 4, wherein at least one aperturethrough the rotor disk is provided in each quadrant between adjacentslots.
 6. A rotary piston pump for fluids comprising: a shaft to rotateabout a longitudinal axis; a rotor centrally secured to the shaft, therotor having a body with a cylindrical surface extending between spacedends; a rotor disk secured at each end of the rotor, each rotor disksecured at a center to the shaft; a housing encasing the rotor and rotordisks and portions of the shaft within an internal cavity, the housinghaving interior end walls adjacent to the corresponding rotor end disks,and an interior sidewall, with fluid inlet and fluid outlet ports in theinterior sidewall, a first portion of the interior sidewall of thehousing being cylindrical and curved with a constant radius over anangle of about approximately 180°, the first portion being spaced aconstant distance from confronting portions of the cylindrical surfaceof the rotor, and a second portion of the interior sidewall of thehousing extending from the extremities of the first portion of theinterior sidewall, and a curvature of the second portion having agreater radius than a curvature of the first portion, the cylindricalsurface of the rotor being proximal to the interior sidewall of thehousing at a point between the fluid inlet and fluid outlet ports aboutmidway along the second portion, the fluid inlet and fluid outlet portsbeing located in this second portion of the interior sidewall of thehousing; two or more equally spaced, radially oriented slots in therotor longitudinally extending across the cylindrical surface of therotor body; two or more similar vanes, each vane having internal andexternal edges extending between sides, each vane slidably seated in oneof said slots, each vane movable radially in the corresponding slotbetween an extended position with the external edge of the vane adjacentthe interior sidewall of the housing, and a retracted position whereinthe external edge of the vane does not extend beyond the cylindricalsurface of the rotor, the vanes being spaced from adjacent vanes aboutthe rotor such that there is always a vane positioned between the fluidinlet and fluid outlet ports; a plurality of slots in the rotor disksaligned with the rotor slots and slidably receiving the sides of thevanes; the rotor disks, the housing and the vanes constructed so that,during operation of the rotary piston pump, fluid entering the housingthrough the inlet port is carried by the rotor, in each of compartmentsformed between adjacent vanes, the rotor surface between the vanes, therotor disks and the corresponding portions of the end walls and interiorsidewall of the housing, until the adjacent vanes encompass the outletport where the fluid is allowed to leave the housing, a pair ofconfigured depressions positioned in each of the end walls, open towardsthe corresponding rotor disk, ports at the bottoms of the slots in therotor disks passing through the rotor disks to provide fluidcommunication between lower portions of the rotor disk slots below thevanes and the configured depressions, and at least one aperture beingprovided in each compartment through each rotor disk, the apertures andconfigured depressions positioned to be intermittently aligned, duringoperation of the pump, so as to permit equalization of fluid pressure inthe compartment and in the configured depressions when the apertures arein alignment with the configured depressions; and the configureddepressions being configured so as to deliver, during operation of thepump, the lesser pressure of fluid being drawn into the compartmentsfrom the inlet port through the slots below the vanes as the vanes passover part of the second portion of the interior sidewall adjacent to theoutlet port so as to urge those vanes inwardly towards retractedposition, and to deliver the greater pressure of the fluid being carriedin the compartments between the inlet and outlet ports through the slotsbelow the vanes when the vanes approach the inlet port and pass over theconstant radius portion of the sidewall so as to urge those vanesoutwardly towards extended position.
 7. A pump in accordance with claim6 further provided with springs urging the vanes to extended position.8. A pump in accordance with claim 6 provided with four slots in therotor disk and four vanes.